Nucleic acid hybridization techniques were used to study the expression of the elastase gene during different stages of development of neutrophil leukocytes in human bone marrow. These studies demonstrated that the elastase gene is expressed only during a short period of time during neutrophil development, at the promyelocyte stage. Thus, the expression of the neutrophil elastase gene is likely under very tight control, and is different than that for other constituents of the neutrophil granules.